Propeller vibration damping means



z- 24, 1948. J. G. BAKER 2,447,628

PROPELLER VIBRATION DAMPING MEANS Filed June 6, 1 942 2 Sheets-Sheet 1 ATTORNEY Patented Aug. 24, 1948- PROPELLER VIBRATION DAMPING MEANS John G. Baker, Evansville, Wis., assignor to United Aircraft Corporation, East Hartford,

Conn., a corporation of Delaware Application June 6,1942, Serial No. 448,041

This invention relates to improvements in aeronautical propellers with particular reference to vibration controlling means, as disclosed in United States Patent No. 2,144,428 issued January 17, 1939, to Erie Martin for Aeronautical propeller having vibration controlling features.

A further object resides in the provision of an improved aeronautical propeller of the character indicated having flexible connections between the blades and the shaft-mounted portion of the propeller hub, giving the. blades alimlted freedom of resilientlyresisted movement relative to the shaft-mounted hub portion. and means for frictionally damping the relative movements between the blades and the hub.

A still further object resides in the provision of an improved aeronautical propeller of the character indicated in which the shank ends of the blades are given a limited freedom of resiliently resisted'movement relative to the propeller shaft. and in which means is provided for frictionally damping the component of the blade movement in the direction of the axis of the propeller shaft.

Other objects and advantages will be more particularly pointed out hereinafter or will .become apparent as the description proceeds.

Claims. (Cl. 170-162) propeller drive shaft of an engine, not illustrated. A hub spider I2 is mounted on shaft ill by suitable means such as a rear cone II, a front cone IS, a front cone nut l8, and splines 20 between shaft lli and spider l2. The spider is provided with a plurality of elongated flexible arms 22, one for each blade 24. Each arm 22 extends through the hollow shank end of the blade and is provided at its outer end with a spherical knob 28 upon which is mounted a split crosshead 28 slidable in a tubular guide Ill secured in the blade.

The shank of blade 24 is provided with an outwardly extending flange 32 upon which is seated an anti-friction thrust bearing 34 which bears against a flange 36 formed on a split barrel member 38 surrounding the blade shank. This type In the accompanying drawings, in which like reference numerals are used to designate similar parts throughout, there is illustrated a suitable mechanical embodiment for the purpose of disclosing the invention. The drawings, however, are for the purpose of illustration only and are not to be taken as limiting or restricting the invention as it will be apparent to those skilled in the art that various changes in the illustrated embodimentmay be resorted to without in any way exceeding the scope of the invention.

In the drawings, Fig. 1 isa longitudinal view, partly sectional, of an aeronautical propeller constructed according to the invention, and

Fig. 2 is a longitudinal sectional view on an enlarged scale of the hydraulic mechanism for frictionally damping'the vibrational movements of the propeller blades.

The present invention permits limited freedom of resiliently-resisted movements between the propeller blades and the propeller drive shaft and means for frictionally damping such blade movements to thereby absorb the vibrational energy and reduce both the amplitude of vibrational movements and the intensity of the vibrational forces.

Referring to the accompanying drawings and particularly to Fig. 1, the numeral I0 indicates a -lariyil lustratedinFig.2.-

of blade retention means is ell known to the art and has been shown for convenience in the illustration of the invention but it is to be understood that the invention is in no way limited to the particular type of blade retention means so illustrated and described.

The hub barrel 38 is axially slidable on spider i2 and is provided at its rearward end with a flange 40 cooperating with a packing ring 42 to provide a fluid seal between the barrel member and the spider. Suitable packing rings, one of which is indicated at 44, are also provided in the hub barrel around the shank of each blade. The front end of the hub'barrel is closed by a dome 44 to make the hub a tight receptacle within which fiuid may be retained for lubricating the various working parts of the propeller pitch changing mechanism and for use-in the damping device. A seat for the inner end of the blade is provided by bearing members 48 and 50 which have portions extending within the cavity in the blade shank and portions overlying the inner end surface of the blade and bearing on suitable blade supports such as the somewhat resilient non-metallic blocks, one of which is indicated at 52, included within the'hub barrel 38 between the blades.

The blades are rotated in pitch changing directions by suitable means well known to the art and including gear sectors, one of which is indicated at 54, secured to the inner ends of the blades and meshing with a master gear 56 lOtRiSr able about the axis of the shaft ill by suitable mechanism which may include the piston 58 and the cylindrical cam members 50 and 62, particu- For a detailed illustration and description of a suitable pitch changing mechanism reference may be had to United States Patent No. 2.174.717. issued October 8, 1939. to Frank W. Caldwell et al..

for Multiposition controllable pitch propeller, or-

and rotatable relative to the hub spider I2, it is apparent that the hub-included end of the blade may move relative to the hub spider both axially and rotationally by an amount limited by the space 04.

The shank end of. the blades may move bodily under the excitation of vibrational forces against the resistance of the resilient arms 2-2. This provides a vibration-induced movement of the blades at a place where a damping device can be connected. The arrangement permits a substantial absorption of vibration energy by providing a vibration-induced movement of the propeller blade shanks and the associated hub barrel and then converting a substantial portion of the energy of this movement into fluid friction by means of a suitable damping (pumping) device secured to the hub barrel. .which 'is, in turn. closely associated with the shank ends of the propeller blades. I

The damping mechanism is particularly illustrated in Fig. 2, in which the dome 40, secured to the hub barrel by the threaded connection (Fig. 1), transmits vibration induced movements of the hub barrel through dome extension 80 and annular connector. to a piston rod 12 secured at one end to the dome extension 00 by means of shoulder 14 and clamp nut 16. While the drawings show a dome having a separate extension and an annular connector, it is to be understood that a one piece dome member extending from the hub barrel to the piston rod 12 may be utilized if desired.

Intermediate its length the piston rod 12 is somewhat enlarged to provide a bearing portion I0 slidably mounted in a bearing 00 carried by a cylinder head 02 which closes the open end of a cylinder 04 within the open, forward, end of tube 00. The tube is secured at its opposite or rearward end to a tubular member 00 which is in turn rigidly secured to the forward end of the propeller shaft I0 by suitable means such as threads 00 in Fig. 1. Thus cylinder 04 and cylinder head 02 are held against axial movement relative to the propeller shaft I0 and the hub spider I2. Longitudinal slots 02 lengthwise of tube 00 make this tube sufllciently flexible to accommodate any slight misalignment between tube 00 and dome extension 00. Cylinder 84 is provided at its forward end with an outwardly extending flange 84 between cylinder head 02 and a ring 00 secured to the end of the tube 00 by a snap ring 00. Screws I00 threaded into ring 00 and passing through the cylinder head and flange l4 serve to clamp these members together and rigidly secure the cylinder and 0311- inder head to the outer end of tube 00.

Within cylinder 04 piston rod 12 carries a piston I02. The end of the piston rod to the left of the piston is provided with a bearing portion I04 slidable in a bearing I00 integral with cylinder 04 so that the areas of the working surfaces on 13th sides of the pi ton I02 are substantially q Since cylinder 04 is rigidly connected by tubes 00 and 00 to the propeller shaft and the hub spider I2, and since piston rod 12 is rigidly connected through dome 40 to hub barrel II and the shank ends of the propeller blades, the above mentioned axially slidable and rotatable movements, in clearance 84, of the blade shank ends relative to the hub spider by reason of the resiliency of spider arm 22, will cause piston I02 to reciprocate axially and rotate in cylinder 04. The piston I02 and cylinder 04 are relatively freely rotatable but axial reciprocation is resisted by thefollowing mechanism. The cylinder has two fluid inlet ports, as indicated at I01 and I00, located one at each end of the cylinder. The ports are controlled by check valves H0 and H2 respectively. With this arrangement, when the piston moves to the right as viewed in Fig. 2 fluid will be drawn into the left end of the cylinder through the port I0! and check valve H0, and when the piston moves to the left fluid will be drawn into the right hand end of the cylinder through port I00 and check valve I I2. This fluid such as oil is drawn from thelubricating fluid supply contained in the propeller hub includin the dome 48. As the propeller rotates the fluid is forced outwardly by centrifugal force, tending to leave a core of air along the rotational axis of the propeller hub. The inlets to valves 0 and 2, however, are located at radial distances from the axis of rotation of the hub sufficient to maintain these inlets at all times in-the body of fluid contained in the dome so that air will not ordinarily be drawn into cylinder 04. As the check valves prevent the return flow of fluid from the cylinder through the ports I01 and I00 to the interior of the dome other means must be provided to vent the trapped fluid in order exterior of the piston rod within dome extension 00. A similar channel I20 leads from the right hand end of the cylinder to a control valve I22, and a vent I24 leads from valve I22 to the exterior of the piston rod I2 within the dome extension Thus, when piston I02 moves to the left as viewed in Fig. 2, while fluid is being drawn into the space between the piston and the cylinder head 02 through port I00 and check valve H2, at the same time fluid will be expelled from the other end of the cylinder through channel II4. control valve III and vent Ill. Similarly, when the piston moves to the right fluid from the space between the piston and the cylinder head will be expelled through the channel I20.

The outlets of i control valve I22 and vent" I24. vents III and I24 are relatively close to the axis of rotation of the propeller and may come within the core of air which may surround this axis. but, since the control valves Iii and I22 act as check valves to prevent any fluid entering the cylinder through the channels H4 and I20, no air will be drawn into the cylinder from that source. This arrangement of valves renders the piston and cylinder mechanism in eflect a pump which under the actuation of vibration-induced movements of the shank ends of the propeller blades withdraws fluid from the interior of the dome through check valves H0 and H2 and returns it to the dome through control valves II. and I22. This circulation of fluid prevents any undue increase in the temperature of the fluid used for damping the movements of thepiston I02, and also tends to eliminate from the cylinder any air that may be brought into the cylinder entrained with liquid contained in the propeller hub.

The damping effect of the piston and cylinder device may be regulated by adjusting control valves IIS and I22. This adjustment may be accomplished by the screws I26 and I2! which bear against compression springs I2. and I22 which, in turn, bear on the ball members of the control valves. Extensions I and I36 on screws I25 and I28 serve to limit the maximum opening of the control valves- For convenience in ad- Justment, screws I26 and I28 are extended outwardly to the end of the piston rod 12 where they are provided with suitabletool slots and covered with a screw cap I28. While adjustable.

control valves have been illustrated and hereinabove described it is to be understood that the invention is not necessarily limited to such an arrangement since it is conceived that once the characteristics of a particular propeller organization were known, fixed valves of the proper restriction could be provided which would function satisfactorily for all propellers of that Darticula'r size and type. a

From the above description .it will beapparent that the fluid damper has substantially no tendency to rebound or spring back, but opposes or resists such return movement and is held by fluid friction in any position in which it may come to rest and is, therefore, a nonresilient or inelastic damper as distinct from a resilient damper such as a resilient rubber layer which will store part of the vibration energy as potential energy and may utilize that potential energy to return to its original position upon release of the stress which caused the original movement.

' While a suitable mechanical embodiment for the purpose of disclosing the invention has been hereinabove described and illustrated in the accompanying drawings, it is to be understood that the invention is not limited to the particular embodiment so illustrated and described, but that such changes in the size, shape and arrangement of the various parts maybe resorted to as come within the scope of the sub-joined claims.

Having now described the invention so that Others skilledin the art may clearly understand the same, what it is desired to secure by Letters Patent is as follows:

1. In a propeller having a hub including a portion fixed against axial movement relative to a propeller shaft, and a plurality of blades carried by said hub, fluid actuated propeller pitch changing means including a fluid chamber, a flexible connection between each blade and said hub portion including means resiliently resisting movement of the hub ends of said blades relative to said hub portion, and a fluid pump having one relatively movable part connected with said hub portion and another relatively movable part connected with the hub ends of said blades and having a valve-controlled fluid outlet and inlet connected with said chamber whereby fluid will be taken from said chamber. forced through the pump and returned to said chamber by movements of the hub ends of saidblades relative to said hub portion, said pump having a restricted fluid outlet passage for producing fluid friction to damp the movements of the hub ends of said blades relative to said hub portion.

2. In a propeller having a hub including a portion fixed against axial movement relative to a mamas I propeller shaft, and a plurality of blades carried by said hub, a flexible connection between each blade and said hub portion providing a limited and another relatively movable part connected with the hub ends of said blades and having a valve-controlled fluid outlet whereby fluid will be forced through said pump by movements or the hub ends of said blades relative to said hub portion, said pump having a restricted fluid outlet passage for applying fluid friction to damp the movements of the hub ends of said blades relative to said hub portion; said propeller hub constituting a fluid reservoir and said fluid pump being disposed in said hub substantially concentric therewith with fluid inlet passages having their intake ends radially spaced from the axis of said hub.

3. A propeller rotatable about an axis and having a. two-part hub, one part of said hub being flxed toa driving shaft and the other part of said hub carrying the blades 01' said propeller. said two hub parts being relatively rotatable and relatively movable axially, pitch changing mechanism connected with said blades and the blade carrying part of said hub for changing the pitch of said blades independent of the relative position of said hub parts. damping means. comprising a fluid pump with restricted outlets, connected with both of-said hub parts and actuatable only by relative movements of said hub parts in an axial direction for damping the movements between the hub parts. I

4. In a propeller having a hub including a por. tion fixed against axial movement relative to a propeller shaft, and a plurality of blades carried by said hub, a flexible connection between each blade and said hub portion including means resiliently resisting movement oi. the hub ends of said blades relative to said hub portion, means for changing the pitch of said blades independent of the relative position of said blade ends andsaid hub portion, a sump, and a fluid pump having one relatively movable part connected with said hub portion and. another relatively movable part connected with the hub ends of said blades and having a valve-controlled fluid outlet and inlet connected with a sump whereby fluid will be. taken from said sump, forced through the pump and returned to the sump by movements of the hub ends 01 said blades relative to said hub portion, said pump having a restricted fluid outlet passage for producing fluid friction to damp the movements of the hub ends of said blades relative to said hub portion.

5. In a propeller rotatable about an axis and having a hub and a plurality of blades carried by said hub, a flexible connection between each blade and said hub including means resiliently resisting movement of the hub ends of said blades relative to said hub in directions perpendicular to the major axis of each blade, and friction damping means carried by said hub and cperatively connected with the hub ends of said blades, and actuated by relative movement of said hub and the hub ends of said blades in the direction of the axis of rotation of said propeller but unaffected byrelative rotation of said hub and the hub ends of said blades for frictionally damping movements permitted by said resilient connections. said friction means comprising an expansible chamber de vice having one part connected with the hub ends auaeae 7 01' said blades and another part held against axial movemiant relative to the hub, said device having restricted fluid passages leading from the interior thereof.

6. An aeronautical propeller having a hub adapted to be mounted for rotation about an axis. a plurality of blades carried by said hub, a connection having a limited freedom of movement between each blade and one portion of said hub, said connection being resilient and flexible cir-' cumierentially of, and in opposite directions parallel to, said axis and including means resiliently resisting movement between the hub end or each blade and said hub portion circumierentially about said axis and parallel to said axis, and substantially inelastic friction damping means connected with the hub ends oi! said blades resisting and frictionally damping all movement in both directions parallel to said axis.

7. An aeronautical propeller as claimed in claim 6 in which said friction damping means comprises a pair of-concentric, telescoped, cylindrical members arranged concentric with said axis and including friction means resisting relative axial movement of said members.

8. A propeller as claimed in claim 7 in which said pair of members are substantially freely rotatable relative to each other.

9. An aeronautical propeller having a hub adapted to be mounted for rotation about an axis,

, a plurality of blades carried by said hub, a connectlon having a limited freedom of movement between each blade and one portion of said hub, said connection being resilient and flexible circumierentially of. and in opposite directions parallel to, said axis and including means resiliently resisting movement between the hub end of each blade and said hub portion circumi'erentiaily about said axis and parallel to said axis, and friction damping means resisting and irictionally damping movement of the hub ends or said blades in both directions parallel to said axis. said triction damping means 7 member of said pair with the hub ends of said blades to impart movement or said blade ends parallel to said axis to said one member, and means restraining the other member 0! said pair against such movement of said one member. and means i'rictionally resisting axial movement of said members relative to each other.

I 10. A propeller as claimed in claim 9 in which said pair 01 members are substantially freely rotatable relative to each other.

some a. BAKER.

nnrannncss crrnn The following references are of record in th die of this patent:

UNITED STATES PATENTS Number Name Date 431,387 McHugh July 1, 1890 1,134,224 Phillips Apr. 6, 1915 1,242,195 Johanson Oct. 9, 1917 1,458,814 Focht June 12, 1923 1,930,380 Binks Oct, 10, 1933 r 1,952,798 Havill Mar, 27, 1934 1,965,742 Junkers July 10, 1934 2,067,109 Viale et al. Jan. 5, 1937 2,112,797 Tyler Mar. 29, 1938 2,144,428 Martin Jan. 17, 1939 2,245,251 Chilton June 10, 1941 FOREIGN PATENTS Number Country Date 48,916 France June 21, 1938 (Addition to No. 817,252) 289,344 Italy Oct. 13, 1941 332,646 Great Britain July 28, 1930 427,503 France Apr. 5, 1911 660,874 France Feb. 25, 1929 

